Silver salt diffusion transfer method



United States Patent Int. (:1. G03c 5/54 US. C]. 9629 6 Claims ABSTRACT OF THE DISCLOSURE In a silver salt diffusion transfer method in which an image is formed by exposure on a silver halide emulsion layer carried by a negative material and the exposed negative material is moistened with a liquid for effecting development of the image which is transferred to a receiving material by subjecting the negative material to compression in contact with the receiving material, the invention proposes to moisten uncoated receiving material immediately prior to the contact with the negative material with an aqueous liquid containing reduction nuclei or substances forming reduction nuclei and silver salt solvents. Hexachloroplatinic (IV) acid and/or gold (III) chloride hydrochloride are the preferred substances.

The invention relates to a silver salt diffusion transfer method making use of a negative material, having a silver halide emulsion layer on which an image is formed by exposure, and a receiving material, to which the image is transferred, wherein the exposed negative material is moistened with a liquid effecting the development and is subjected to compression together with the moistened receiving material, which is made of paper, felt or textile material.

In German patent specification No. 764,572, the socalled silver salt diffusion method is described and it is stated that various substances are used as the receiving material, e.g. uncoated papers, textile sheets, wood, Celluloid and other plastics materials and the like. However, it is pointed out that by the term material the invention refers to any sheet-form material.

The aforesaid specification further discloses that the transfer can be aided by the presence of substances favoring diffusion. Moreover, the diffusing or diffused silver halide can be developed imagewise without exposure, whereby this development is aided by added nuclei or reactants. By way of example, the developed image is transferred to a baryta paper or to a textile underlayer or support, which has been moistened in the same bath as the silver halide material. In carrying out the method in practice, as it has been developed for industrial utilization with the use of copying materials in sheet form, a separate positive or receiving layer has sometimes been provded in which the reduction nuclei are arranged. This layer is usually arranged on a special support so that the layer and support form the receiving material.

It is also known that this receiving layer can be used independently of a support and, by way of example, can be applied as a cover layer on the negative layer. Such an embodiment is described in German patent specification 1,171,740 and referred to as a colloidal cover and receiving layer. No reduction nuclei need be contained in this layer. However, according to German patent specification 1,171,740, reduction nuclei are supplied to the colloidal receiving layer by means of the processing liquid. According to the cited specification, known reduction nuclei are sulphides, selenides, polysulphides, polyselenides, thiourea, mercaptans, stanno halides, heavy metals or their salts, as well as fogged silver halides and sulphides of heavy metals such as antimony, bismuth, cadmium, cobalt, lead, nickel and silver. For this purpose, the heavy metals, for example, silver, gold, platinum, palladium and mercury, especially in colloidal form, are considered the most effective. The noble metals are particularly preferred.

In the method according to patent specification 1,171,- 740, the image-receiving layer is thus provided as a cover layer on the negative, and a sheet of material is provided for receiving the image developed in the cover layer. Since according to patent specification 764,572 the diflicultly soluble silver compound or colloidal silver, which is produced in the receiving layer, is nondiffusable, the colloidal cover or image-receiving layer containing the developed image is also transferred during the transfer to the receiving sheet, paper or the like.

In other copying or transfer methods, it has proved to be possible to transfer a usable image to a normal sheet of paper without using a positive layer. These, however, are physical methods, for example the electrophotographic method may be involved.

German patent specifications 764,572 and 1,171,740 are based on the use of reduction nuclei, such as have been used in the silver salt diffusion method generally known as the Copyrapid method.

If the reduction nuclei according to patent specification 1,171,740 are provided in the processing liquid, which not only serves for carrying out the developing, but also for the complex salt formation of the unexposed and undeveloped silver halide, then the same limitations exist, in respect to the stability of such solutions, as are known to exist in developers used in the silver salt diffusion method. These limitations are due to the simultaneous presence of air oxidation products, used and unused developing substances, the rising content of silver halide solvents caused by the increased number of copies and silver halide complex compounds which diffuse into the solution and may be active as reduction nuclei.

The basic task of the invention is to find a method by which the production of a positive image on an uncoated support or layer is made technically possible by the silver salt diffusion method, while at the same time the liquids used superior stability and make possible a very large number of prints without replacement or replenishment. The expression uncoated paper designates a support containing no film-forming colloids, but for which only a wetting with an aqueous solution is provided. More over, the invention at the same time aims to use simple and cheap materials, one of which is used uncoated, and which especially do not involve the problem of a plurality of coatings on a support. This is so because with a plurality of coatings, there is the possibility that, during long storage times and/or through varying influence of atmospheric moisture and temperature, an impairment of the layers can result if special binders are not provided.

The problem has been solved by the invention in that the receiving material of the nature described is moistened before being combined or compressed with the negative transfer material, with a liquid that is different from the one for negative development, and containing in aqueous solution reduction nuclei or substances forming reduction nuclei and a silver salt solvent as well as a wetting agent.

The invention has the advantages that no film-forming colloid-receiving layer is used and that ordinary diffusion negative materials as available on the market can be used, whereby the processing liquids can be employed according to their composition in such a way that excellent stability is effected while at the same time a large number of prints can be produced.

It has thus surprisingly been found that prints of excellent quality are produced when the receiving material and the negative materials are moistened with dfferent liquids, and that, contrary to the prior belief, no film-forming colloid receiving layers are necessary. A further important advantage of the invention is that with the use of customary industrial diffusion negative materials, for example of the Copyrapid dry negative type, prints of superior quality are produced although uncoated receiving material is used. Copyrapid is a trade name of Agfa-Gevaert A. G. Therefore, no expensive specially prepared papers have to be used.

With reference to the features of the invention, it is important that the term moistening is not understood to designate coating, but a wetting with an aqueous solution of the reactants which have no layer-forming character. According to the invention, it is sufficient, for example, to wet one side of the receiving support. With coatings, it is customary to dry these. According to the method of the invention, which uses a receiving material that, for example, comprises paper, the term moistening essentially means that this receiving material is treated in the moist state, to wit, after it has been moistened with the aqueous solution of the reactants.

For example, a heat copying method is known from German patent specification 1,168,927 in which ordinary paper used as a receiving material is coated before the transfer process. However, in this prior art method the paper is coated with a solid layer which is not influenced by diffusion or transfer, but which assumes a definite color at a stated temperature.

In respect to moistening, it is possible to moisten only one side of the receiving sheet, to wit, that side on which the image is to be formed. The moistening can thus be carried out by any known method, such as spraying, application with. a moistening roller or the like. Advantageously, the receiving material is pressed through the aqueous nuclei containing solution in a known way.

According to a preferred embodiment, commercially available Copyrapid dry negative paper is used as the negative material and, as the developer liquid, an activator suitable for this material. When using other customary silver salt dilTusion negative papers, a customary industrial developer for such papers is used.

With reference to the economy of the method, a significant feature is that, as the processing liquid for the receiving material, a solution with a concentration of only approximately 0.02% of a hexachloroplatinic-(IV) acid and/or a gold (III) chloride hydrochloride is employed. It has been shown that, apparently for the reasons given above, in using such a liquid, far more prints can be produced than if the nuclei themselves are contained in the developing liquid.

Where Within the scope of the invention reference is made to reduction nuclei, then also a combination of different nuclei can be used.

The present invention is distinguished not only in that processing baths are simple, stable and relatively cheap, but in developing for the first time an industrially workable method in which ordinary papers can be used as receiving sheets, without having to provide additional coatings for the negative material. In the latter case, the advantage-of the use of a simple sheet of paper as the receiving material would be practically negated by complication of the neagtive.

It has been found that, when using the inventive method, it is not possible to prefabricate ordinary paper by prior impregnation with the aqueous solution which is provided for the processing of the receiving material, and then to dry the impregnated paper. Such an embodiment does not lead to the desired result.

Thus, in its simplest form, the invention provides not only a new method in which the time of action of the solution on the paper can be adjusted, but it is based on a definite method of procedure in which the receiving material must be moistened with the nuclei containing liquid immediately before pressure contact with the negative transfer material.

The following examples are given for this liquid; in all these examples:

H O-dist. water;

Mirasol-0.5% solution in H O (trade name for wetting agent);

Na S O soln.sodium thiosulphate, 1% in H O;

AgNO soln.l% silver nitrate solution in H O;

Platinum soln.l% dry hexachloroplatinic (IV) acid Gold soln.l% gold (III) chloride hydrochloride hydracid, yellow in H O; H(AuCl -4H O.

EXAMPLE I H O 1000 Mirasol l5 AgNO soln 2O N32820:; soln EXAMPLE II H O 1000 Mirasol 15 Gold soln. 2 Na S O soln. EXAMPLE III H O 1000 Mirasol 15 Gold soln. 5 Na S O SOln. 1

EXAMPLE IV H O 1000 Mirasol 15 Platinum soln. 10 Na S O soln. 5 Gold soln. 5

EXAMPLE V H O 1000 Mirasol 15 Platinum soln. 10 N32520:; SOln. 5 Gold soln. 10

To carry out the method, an apparatus with two liquid baths may be used. The transfer material and the receiving material are conveyed through the respective bath before they are carried to a pair of ordinary compression rollers.

Thus the invention creates a two-bath-method with the use of a receiving material which remains uncoated and is only moistened separately and is supplied to the compression rollers in the moist state, while an ordinary negative is used as the negative material. This provides for the first time a practical solution for producing high quality prints with the silver salt diffusion method on a receiving material made of ordinary paper, film or textile.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise Without departing from such principles.

Mirasol is a trade name for a wetting agent, manufactured by Tetenal Fotowerk, Hamburg, Germany and is available on the market.

What is claimed is:

1. In a silver salt diffusion transfer method, in which an image is formed by exposure on a silver halide emulsion layer of a negative material, and the exposed layer of the negative material is moistened with a liquid for effecting development of the image which is transferred to a receiving material by pressing together the layer of the negative material and the receiving material, the improvement which comprises that the receiving material is an uncoated sheet which, immediately prior to contact with the layer of the negative material, is moistened with a liquid containing in aqueous solution hexachloroplatinic (IV) acid and/or gold (III) chloride hydrochloride and silver salt solvent.

2. The improvement according to claim 1, in which the liquid for moistening the receiving material comprises a solution containing about 0.02% of a hexachloroplatinic (IV) acid and/or of a gold (III) chloride hydrochloride.

3. The improvement of claim 1, wherein the uncoated sheet is a paper, film or textile sheet.

4. In a silver salt diffusion transfer method, wherein an image is formed by exposure on the silver halide emulsion layer of a negative sheet and the thus exposed negative sheet is developed by a developer liquid, whereupon the developed image is transferred by pressure contact to a receiving sheet, the improvement which comprises that the receiving sheet is uncoated sheet material which, im-

mediately prior to the pressure contact with the negative material is moistened with a liquid of diiferent composition than said developer liquid, said liquid comprising an aqueous solution containing (a) a silver salt solvent, and

(b) hexachloroplatinic (IV) acid and/or gold (III) chloride hydrochloride.

5. The improvement of claim 4, wherein the uncoated sheet material is ordinary paper.

6. The improvement of claim 4, wherein the silver salt solvent is sodium thiosulfate.

References Cited UNITED STATES PATENTS 2,352,014 6/1944 Rott 9629 2,740,717 4/ 1956 Yutzy et a1 96-29 3,179,517 4/1965 Tregillus et al 96-29 GEORGE F. LESMES, Primary Examiner J. P. BRAMMER, Assistant Examiner 

